Recently, as smartphones and tablet PCs are widely used and multimedia communications of high capacity are activated, mobile traffic increases rapidly. The increasing tendency of the mobile traffic in the future is expected to increase about twice each year. Since most of the mobile traffic is transmitted through a base station, communication service providers are currently confronted with serious network overloads. In order to handle the increasing traffic, the communication service providers increase network equipment investment and commercialize the next generation mobile communication standards (e.g., WiMAX, LTE (long term evolution), etc.) for efficiently handling lots of traffic in a hurry. Yet, in order to bear the amount of traffic expected to increase further rapidly, it is time to seek for other solutions.
D2D (device-to device) communication is a distributive communication technology for directly delivering traffic between adjacent nodes without using such an infrastructure as a base station. In D2D communication environment, each node such as a mobile terminal and the like searches for another user equipment physically adjacent to the corresponding node by itself, establishes a communication session, and then transmits traffic. Thus, since the D2D communication can solve the traffic overload problem in a manner of distributing the traffic focused on a base station, the D2D communication is spotlighted as an elementary technology of the post 4G next generation mobile communication. Such a standardization organization as 3GPP, IEEE and the like is promoting D2D communication standard enactment based on LTE-A or Wi-Fi. And, such a company as Qualcomm and the like is developing an independent D2D communication technology.
D2D communication is expected to create new communication services as well as to contribute to increase performance of a mobile communication system. And, the D2D communication can support adjacency based social network services or such a service as a network game and the like. If a D2D link is utilized as a relay, it is able to solve the problem of connectivity of a user equipment in a radio shadow area. Thus, the D2D technology is expected to provide new services in various fields.
Actually, D2D communication technologies including IR (infrared ray) communication, Zigbee, RFID (radio frequency identification), NFC (near field communications) based thereon are widely used nowadays. Yet, since these technologies can support communications for special purposes within a very limited distance only, it may be difficult to exactly categorize these technologies into the D2D communication technologies for distributing traffic of a base station.
So far, the D2D communication is described. However, a procedure for transmitting ACK/NACK signal for a data transmission between D2D user equipments to perform an efficient D2D communication on a cellular network and a method of transmitting ACK/NACK on D2D data transmission of transmission resource information and the like have not been proposed yet.